Single turn induction coil



April 20, 1954 N. E. FOXX SINGLE TURN mnucnou c011.

Filed Nov. 29, 1950 NOEBEET E- FOXX A 270 RNA-Y5 Patented Apr. 20, 1954 UNITED STATES ENT OFFICE SINGLE TURN INDUCTION COIL Application November 29, 1950, Serial No. 198,203

8 Claims. 1

This invention relates to induction heating and, more particularly, to an improved method and apparatus for the induction heating of localized areas.

In certain applications of induction heating, such as the seam welding of steel tubing, it is necessary that the induction heating effects be restricted to relatively confined areas.

The present invention is concerned with an induration-heating coil suitable particularly for such applications as the production of steel tubing but, in principle, having a wide range of application.

The coil, or inductor, of the invention comprises a single-turn conductor of heavy cast metal construction. The cross section of the coil varies around the circumference thereof, a constriction or reduction in cross sectional area being formed at one point of the circumference. This construction in cross sectional area around the circumference of the coil is accompanied. by a change in the form of the cross section, the form at the point of constriction being generally paraholoidal with the apex toward the center of the coil. The decrease in cross sectional area causes an increased current density at that portion of the coil while the form of the coil produces a great increase in field intensity in the vicinity of that portion of the coil. As a result, the portion of a work piece passing through the coil which is immediately adjacent the sector of reduced cross section will be heated very intensely while the remainder of the piece will receive very little heat.

An object of the invention is the induction heating of restricted portions of tubing in the manufacture thereof.

An object of the invention is the induction heating of restricted portions of strip material along the length of the strip.

An object of the invention is the provision of an electrical inductor of simple and strong mechanical construction.

An object of the invention is the provision of an inductor for generating localized heating fields which will occupy a minimum of space.

An object of the invention is the provision of a single turn inductor capable of generating concentrated electrical fields.

These and other objects and features of the invention will be more readily apparent from a consideration of the following detailed specification and appended claims, taken in connection with the accompanying drawings, in which:

Fig. 1 is a diagram of the apparatus of the in- 2 vention showing particularly a perspective view of the novel inductor;

Fig. 2 is a cross section of the inductor taken along the line 2-2 of Fig. 1; and

Fig. 3 is a representation in cross section of an alternative form of the inductor.

Referring now to Fig. 1, the invention is illustrated as embodied in apparatus for the buttseam welding of steel tubing. The formed pipe blank it is passed through the inductor I I which generates heat along a seam I2 by induction. The pipe blank then passes to the pressure and reducing rolls which complete the welding and finishing operations.

The inductor II comprises a single-turn conductor of very heavy construction being, preferably, cast of suitable material. The inductor is split at a point of the circumference by a radial gap to accommodate two terminal plates It and it, which may be formed integrally with the body of the coil, or welded or brazed thereto. The terminals of the coil are attached to the terminals I5 and I6 of a high frequency transformer while an insulator I1 serves to provide mechanical support and electrical isolation between the sets of terminals. High frequency energy is supplied by a generator It or other suitable apparatus, the energy being imparted to the inductor II through a transformer I9. The terminals iii and I6 are those of the transformer is, the dual representation being adopted for simplicity.

The inductor II is formed with a recess 2i! which is covered by a strip 2|, welded to the body of the inductor to form a passageway for a coolant. Water may be utilized, circulation being had from an inlet 22, an upper lead pipe through the coil passageway, a lower lead pipe 24 and to the outlet 25. The water may be circulated at any suitable rate to maintain a reasonable temperature over the assembly.

The form of the inductor I I and the manner of variation of the cross section thereof may best be understood by reference to Fig. 2, taken in connection with Fig. 1. As there indicated, the inductor is generally of the form of a ring or tore, the section plane being taken through the longitudinal axis of the inductor, and passing through the plane of minimal cross sectional area, indicated at 26. The external form of the inductor section as indicated at the section 26 is generally paraboloidal in shape, this statement being made in a descriptive sense. The cross section may be formed according to any desired function, the essential requirement being that both sides of the inductor converge to a portion 27 formed by an arc of relatively small radius. Thus, the cross section 26 may be said to be generally ii-shaped. lhe portion 2? must, of course, not be pointed, else arcing will take place.

The cross section of the inductor varies substantially uniformly about the circumference of the inductor in both directions from the minimal section 26. As shown in Fig. 2, the opposing section 28 cut by the sectional plane is of generally rectangular form. The inner surface 29 is, however, somewhat arcuate in order to provide a more uniform spreading of the field extending between the point 2'! and the surface 29. The corners (iii and BI are rounded for a similar reason and to prevent arcing and corona effects.

A preferred modification of the inductor of the invention is shown in Fig. 3, a sectional view similar to that of Fig. 2 being shown. Here, the inner surface of the lower portion of the inductor incorporates a series of corrugations 32. The centerline of the corrugations may be formed along the arc of a circle, the center of the circle being taken at the reduced portion 2? of the upper portion of the coil. It is to be understood that the extent and are of the corrugations diminishes uniformly in both circumferential directions from the lower section 33. Such a manher of construction of the inductor serves to provide an optimum distribution of circulating curlts in the work piece in the portion away from u e region of localized heat. Thus, the localization effect is optimum.

It will be seen that many advantages are inherent in such a form of inductor. In particular, the great strength of the coil renders it durable and avoids the necessity for frequent replacement. Further, the mechanical ruggedness renders the coil stable in electrical operation, a factor of importance where the operating conditions are such as in pipe mills. Finally, a very great concentration of heat may be obtained, so much so as to enable the cutting of bar or pipe stock, if so desired.

The foregoing description is necessarily of a detailed character in order that the specific embodiment of the invention may be completely set forth. It is to be understood that the specific terminology is not intended to be restrictive or confining and that various rearrangements of parts and modifications of detail may be resorted to without departing from the scope or spirit of the invention as herein claimed.

What is claimed is:

1. Apparatus for the induction heating of localized areas comprising a conductor having two ends, and terminals connected to said ends, the said conductor having an annular shape and the two ends being adjacent to and opposite each other, one portion of the conductor being generally v shaped with a rounded vertex directed toward the annular center of the piece and the remaining portion of the conductor having a relatively wide portion on the internal circumference of the conductor, whereby high circulating currents may be induced in portions of work pieces adjacent the V-shaped portion of the conductor and relatively low currents in remaining portions.

2. The invention in accordance with claim 1, the conductor having a cross section varying from a generally V-shape to a generally trapezoidal shape.

3. lhe invention in accordance with claim 1 characterized in that the conductor converges to a generally parabolic shape at one point along the surface and that the inner circumference of the conductor at a point diametrically opposite there to is formed with corrugations therein.

A single turn induction coil for heating a small portion of a Work piece to a relatively high temperature while producing a relatively low heat in the remainder of the piece comprising an annular metallic member having an axial opening adapted to pass the work piece, the body of the member having a constricted portion tapered toward the center of the member and the thickness of the member increasing from the constricted portion circumferentially about the member to a relatively wide portion having a substantial axial extent at the opening, a radial gap through the body of the member and terminal plates joined to the body of the member at the gap for supplying induction currents to the member whereby the induction currents passing through the member are concentrated to a relatively high intensity at the innermost part of the constricted portion of the member and dispersed to a relatively low intensity about the remainder of the member adjacent the opening.

5. A single turn induction coil for heating a small portion or a work piece to a relatively high temperature while producing a relatively low heat in the remainder of the piece comprising an annular metallic member having an axial opening adapted to pass the work piece, the body of the member having a constricted portion tapered toward the annular center of the member and the thickness of the member increasing uniformly in both axial directions from the con-- stricted portion circumferentially about the member to a relatively wide portion having a substantially axial extent at the opening, a radial gap through the body of the member away from the constricted portion and terminal plates joined to the body of the member at the gap for supplying induction currents to the member whereby the induction currents passing through the member are concentrated to a relatively high intensity at the innermost part of the constricted portion of the member and dispersed to relatively low intensity about the remainder of the inner periphery of the member.

6. A single turn induction coil for heating a small portion of a Work piece to a relatively high temperature while producing a relatively low heat in the remainder of the piece comprising a heavy annular metallic member having an axial opening adapted to pass the work piece, the body of the member having a constricted portion tapered toward the annular center of the member and the thickness of the member increasing uniformly in both axial directions from the constricted portion circumferentially about the member to a relatively wide portion having a substantial axial extent adjacent the opening, a radial gap through the body of the member away from the constricted portion, and terminal plates joined to the body of the memher at the gap for supplying induction currents to the member, the portion of the body away from the constricted portion having an arcuate depression along the opening to provide substantially equal current paths about the member from the constricted portion to the relatively wide portion.

7. A single turn induction coil for heating a small portion of a work piece to a relatively high temperature while producing a relatively low heat in the remainder of the piece comprising a heavy annular metallic member having an axial opening adapted to pass the work piece, the body of the member having a portion tapered to a vertex adjacent the opening and the thickness of the member increasing uniformly from the vertex circumferentially about the member to a portion having a substantial axial extent adjacent the opening, a radial gap through the body of the member and two terminal plates joined to the member at the ends formed. by the gap for supplying high frequency induction currents to the member, the internal portion of the member away from the tapered portion having a symmetrical arcuate depression formed therein to make the corresponding portions of the innersurface of the member equi-distant from the innermost part of the vertex of the tapered portion and insure current paths of substantially equal length about the member and in both axial directions from the vertex.

8. The invention in accordance with claim 7, the internal portion of the member being formed with a corrugated inner surface to produce a more uniform axial distribution of the currents along the part of the coil away from the said vertex.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,383,992 Sherman Sept. 4, 1945 2,459,971 Stanton Jan. 25, 1949 2,480,315 Bennett Aug. 30, 1949 2,509,713 Achard May 30, 1950 FOREIGN PATENTS Number Country Date 613,323 Great Britain Nov. 25, 1948 616,117 Great Britain 1- Jan. 17, 1949 767,227 Germany Mar. 3, 1952 

